1. Field of the Invention
The present invention pertains to a method and apparatus for crimping ends of can bodies utilized in cans for beverages or the like.
2. Description of the Prior Art
When manufacturing an aluminum can for beverages, a crimping operation is carried out on the open end of a cylindrical can body having a bottom, which is manufactured by deep drawing, to form a plurality of crimps thereat. The crimps are provided in order to reduce the diameter of the top end to be fitted over the open end of the cylindrical can body, which is great in thickness and hence high in cost, resulting in the reduction in total manufacturing cost of the can.
The crimping operation has hitherto been conducted in a manner as shown in FIG. 1, in which the numeral 1 denotes a male die of a cylindrical shape, while the numeral 2 denotes a female die disposed coaxially around the male die 1 with a gap formed therebetween. The female die 2 is provided with a tapered surface 2A formed on an inner surface thereof to reduce the diameter of the can body at the open end thereof.
The male die 1 and the female die 2 are simultaneously moved forward as illustrated in FIG. 1(a). Then, the male die 1 is stopped when a prescribed length of the male die 1 enters the can body K as illustrated in FIG. 1(b), while the female die 2 is further moved to cause the tapered surface 2A to engagingly fit on the can body K. With this procedure, the open end of the can body K is gradually reduced in diameter, and is moved longitudinally along an outer peripheral surface of the male die 1, which is in a stationary state, to thereby produce a reduced-diameter portion as illustrated in FIG. 1(c). Thereafter, the female die 2 and the male die 1 are both moved backward when the length of the reduced-diameter portion reaches a prescribed value, and the can body K is conveyed to the next step as illustrated in FIG. 1(d). The repetition of the aforesaid procedure results in the formation of a plurality of crimps in the can body K and the reduction of the diameter at its open end.
A conventional apparatus for practicing the aforesaid method includes a crimping mechanism comprised of inner and outer cylinders for supporting the male and female dies 1 and 2, respectively, for sliding movement. One of the conventional crimping mechanisms is constructed so as to work as follows. First, only the outer cylinder is driven by a single cam while keeping the inner cylinder pressed against a forward end portion of the outer cylinder by means of a spring or the like, and when the outer cylinder advances a prescribed length, only the outer cylinder is caused to advance a prescribed length while preventing the movement of the inner cylinder by means of a stopper. Thereafter, the outer cylinder is caused to move backwards together with the inner cylinder. In another crimping mechanism, the male die 1 and the can body K are driven by separate drive sources while keeping the female die 2 stationary, to thereby carry out the method as illustrated in FIG. 1.
In the aforesaid crimping method, however, when the open end of the can body K is reduced in diameter by the female die 2 to extend along the outer peripheral surface of the male die 1 a friction force is exerted on the male die 1 and the extended portion of the can body in a opposite directions, so that there may occur wrinkles or buckles in the reduced portion due to the friction. Therefore, if the thickness of the wall of the can body K is reduced or if the working speed of the manufacturing apparatus is increased, defects such as wrinkles and buckles tend to occur more frequently, and hence it is difficult to lower manufacturing costs by reduction of the thickness of top end K, and it is also difficult to increase productivity by speeding up processing.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
Specifically, in the mechanism which drives the inner and outer cylinders by a single cam, the aforesaid disadvantage cannot be avoided, whereas in the mechanism which drives the male and female dies 1 and 2 separately, it has bee difficult to completely synchronize the movement of these dies to move them at a precise amount of movement and speed, resulting in low operational precision and reliability. Furthermore, since separate drive sources are provided for the male and female dies 1 and 2, respectively, the apparatus is of an intricate construction, resulting in high costs.